1. Field of the Invention
The present invention relates generally to data processing systems and, more specifically, to a computer-implemented method for the balancing of data tape cartridge utilization in automated tape libraries with pass-through mechanisms.
2. Description of the Related Art
With the continuously growing amount of information and new regulations for data archiving, more and more data needs to be managed and stored as back up. Typically, tape storage is still the most used backup medium for larger volume of data. With the current focus towards “green information technology,” tape as backup medium may become even more important in the future. Capacity and environmental aspects, together with the excellent disaster recovery attributes of tape storage (such as placing data on tape cartridges in offsite vaults), will typically preserve the importance of data stored on tape media relative to other media.
In enterprise data centers, automated tape libraries are commonly used to provide a backup capability for data. Automated tape library systems are generally available from a number of vendors. The automated tape libraries can house hundreds of tape drives and thousands of data tape cartridges. In some cases, automated tape libraries, or so-called tape silos, include a “pass-through mechanism.” For example, the entire library consists of multiple library strings, or tape silos, that are connected to each other via a mechanism that allows traversal of tape cartridges from one tape library string to another tape library string. Each library string, or tape silo, has an inventory of cartridges and tape drives. The inventory of tape cartridges and tape drives differs between the different library strings and tape silos. Cartridges may be one of two types. A first type is a “scratch” type, or empty cartridge. The second type is a “data/private” type in which the tape cartridge contains valid data. Scratch cartridges are typically used for new backups.
During backup or restore operations from tape cartridges, a situation can occur over time in which in one library string, or tape silo, all of the drives are statistically used more frequently than drives in another library string, or tape silo. In an extreme case, mount requests cannot be executed because all drives in the library string are busy at the same time. In such cases, the backup server has to wait until one drive becomes free. Such an event typically implies an impact on the backup application, and therefore, users of the library because the backup operation may not complete in time.
Solutions have been provided to move tape cartridges between library strings in the situation when no drive is available for a mount in the current string. The movement of the tape cartridges, however, occurs at the time when the backup operation started, which causes a delay in the backup operation.